Technical Field
Embodiments of the invention relate generally to magnetic resonance imaging (“MRI”) systems, and more specifically, to a system and method for hyperpolarizing a substance.
Discussion of Art
MRI is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of objects having substantial populations of atomic nuclei that are susceptible to nuclear magnetic resonance (“NMR”). Many MRI systems use superconductive magnets to scan a subject/patient via imposing a strong main magnetic field on the nuclear spins in the subject to be imaged. The nuclear spins are excited by a radio frequency (“RF”) signal/pulse transmitted by a RF coil at characteristics NMR (Larmor) frequencies. By spatially disturbing localized magnetic fields surrounding the subject and analyzing the resulting RF responses from the excited nuclear spins as they relax back to their equilibrium state, a map or image of the nuclear spins responses as a function of their spatial location is generated and displayed. An image of the nuclear spins response provides a non-invasive view of a subject's internal structure.
In certain MRI procedures, referred to as Hyperpolarized MRI, e.g., Metabolic MRI, it is sometimes advantageous to inject a subject/patient with a hyperpolarized substance. The term “hyperpolarized,” as used herein with respect to a substance, refers to a state of the substance in which the number of nuclear spins of the substance having a polarized state is greater than the number of nuclear spins of the substance having a polarized state at thermal equilibrium conditions. Due to the high percentage of nuclear spins having a polarized state, a hyperpolarized substance may generate an MR signal more than 10,000 times stronger than many non-hyperpolarized substances. Thus, many hyperpolarized substances are effective MRI tracers.
Methods of producing hyperpolarized substances often involve lowering the temperature of a substance in the presence of persistent radicals within a strong magnetic field, and subsequently irradiating the substance and persistent radicals with microwaves. As used herein, the term “persistent radical” refers to an atom and/or molecule that has a free electron and remains within a substance for an indefinite amount of time, and which is not readily removable from the substance without de-hyperpolarizing the substance. Following a Boltzmann distribution, the electron spins of the persistent radicals become highly polarized at low temperature within the strong magnetic field, and the microwaves transfer polarization from the persistent radicals to the nuclear spins of the substance.
Many hyperpolarized substances created by such methods, however, often have short life spans, i.e., the amount of time such substances are in a hyperpolarized state. In particular, the persistent radicals themselves contribute to de-polarization of the substance over time. Accordingly, it is usually necessary to create a hyperpolarized substance at the same location/site at which an MRI procedure utilizing the hyperpolarized substance is performed. Many systems capable of creating hyperpolarized substances, however, are often expensive and/or require a large amount of space. Additionally, it is also usually necessary to create a hyperpolarized substance within a short time period of beginning an MRI procedure which utilizes the hyperpolarized substance. Thus, many systems for creating a hyperpolarized substance are often limited in the number of MRI procedures that they can service in a single day.
What is needed, therefore, is an improved system and method for hyperpolarizing a substance.